Circuit Arrangement for Overtemperature Detection

ABSTRACT

A method and system is provided for retrieving information about operational data from a plurality of building systems and service and maintenance information for a plurality of building sites. A customer web portal is provided with a database for storing the operational data and the service information allowing users to more readily generate reports and obtain service related information for a plurality of sites without having to maintain separate database systems at remote locations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims the benefit of, priorapplication Ser. No. 11/731,765, filed on Mar. 29, 2007, which in turnclaims priority from German patent application no. 10 2006 014 523.2-33,filed Mar. 29, 2006, the contents of which are incorporated herein byreference.

TECHNICAL FIELD

The invention relates to a circuit arrangement for overtemperaturedetection in transistors, particularly power transistors.

BACKGROUND

Power transistors are transistors which provide for large current andvoltage amplitudes and are thus suitable for directly operating loadswith relatively large powers. Power transistors are used, for example,in output stages and switching stages for industrial electronics andmotor vehicle engineering.

In this context, the temperature of a power transistor represents asignificant factor for its functional capability. An overtemperature ofthe power transistor, generated, for example, by a higher ambienttemperature or by malfunction such as a short circuit of loads, can leadto it being damaged or destroyed and in addition can also lead toimpairment or even destruction of the load. It is essential, therefore,to detect any overtemperature of power transistors in time and reliablyin order to be able to take suitable measures such as, for example,switching off the transistor or the load before critical temperaturevalues and thus the damage limit are/is reached.

To determine the temperature of a semiconductor component, a temperaturesensor can be attached to the package of the semiconductor component orto its semiconductor body/chip. It can be inappropriate that the sensorand the actual semiconductor component are two separate components, as aresult of which the sensor only detects the temperature externally onthe semiconductor component which can deviate considerably from thetemperature in the interior of the semiconductor component and, inaddition, has an unwanted inertia in the case of rapid temperaturechanges in the interior of the semiconductor component. It is preciselythe temperature in the interior of the semiconductor body, however,which is relevant to the determination of critical operating states.

There is a general need for a circuit arrangement with a temperaturesensor which is integrated into the same semiconductor body like thepower transistor, where the temperature sensor reliably provides avoltage dependent on the temperature in the interior of thesemiconductor body.

SUMMARY

In one embodiment of the invention a diode structure is additionallyintegrated into a semiconductor body. The diode structure is fed with acurrent in its forward direction from a current source. The voltage dropacross the diode structure is dependent on the temperature of the diodestructure and thus on the temperature of the transistor structure, andcan therefore be used for overtemperature detection by an evaluatingunit, wherein the protection of the power transistor and of theco-integrated temperature sensor due to undesirable destructionguaranteed by the evaluating unit.

Using a diode structure integrated into the semiconductor body, which isfed in the forward direction (not in the reverse direction) by a current(not by a voltage) provides for a large signal swing, and due to thefact that a switching element located in the evaluating unit activelyproduces a short circuit between the bulk of the semiconductor body andthe source of the power transistor when this is required due to theoperating state of the power transistor or of the evaluating unit, whichfor the first time enables the arrangement according to at least oneembodiment of the invention to be used for overtemperature detection inn-channel LS switches and in p-channel HS switches.

Further advantages can also be obtained if the (for example separate,particularly external) evaluating unit for detecting the overtemperatureand the power transistor structure are thermally decoupled from oneanother, which has a positive influence on the accuracy and reliabilityof the evaluating unit, and due to the fact that the influence of theambient temperature on the power transistor structure and the evaluatingunit can be taken into consideration.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, instead emphasis being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereference numerals designate corresponding parts. In the drawings:

FIG. 1 shows the chip-on-chip technology for measuring the temperature;

FIG. 2 shows the measurement of the leakage current of an integrateddiode in the reverse direction at the n-channel HS switch;

FIG. 3 shows the measurement of the diode voltage of a forward-polarizeddiode on the exemplary n-channel HS switch;

FIG. 4 shows an n-channel LS switch and a parasitic diode structure;

FIG. 5 shows a p-channel HS switch and a parasitic diode structure;

FIG. 6 is a circuit diagram of a temperature sensor integrated in asemiconductor body, with parasitic diode structure and a separateevaluating unit, taking into consideration the ambient temperature,according to a first embodiment of the invention;

FIG. 7 is a circuit diagram of a temperature sensor integrated in asemiconductor body, with parasitic diode structure and a separateevaluating unit with voltage/current converters according to a secondembodiment of the invention;

FIG. 8 is a circuit diagram of a temperature sensor integrated in asemiconductor body, with parasitic diode structure and a separateevaluating unit with monitoring of the voltage at the drain terminal ofthe power transistor structure according to a third embodiment of theinvention; and

FIG. 9 is a circuit diagram of a temperature sensor integrated in asemiconductor body, with parasitic diode structure and a separateevaluating unit with external activation of the measurement according toa fourth embodiment of the invention.

DETAILED DESCRIPTION

To determine the temperature of a semiconductor component 100, atemperature sensor 101 can be attached to the package of thesemiconductor component 100 or to its semiconductor body/chip (see FIG.1). Sometimes it can be useful that the sensor and the actualsemiconductor component are not two separate components, as a result ofwhich the sensor only detects the temperature externally on thesemiconductor component which can deviate considerably from thetemperature in the interior of the semiconductor component and, inaddition, has an unwanted inertia in the case of rapid temperaturechanges in the interior of the semiconductor component. It is preciselythe temperature in the interior of the semiconductor body, however,which is relevant to the determination of critical operating states.

To determine the internal temperature of a semiconductor component,diode structure may be provided in the same semiconductor body in whichthe semiconductor component is integrated, the diode structure beingconnected to a supply voltage.

FIG. 2 shows an example of an n-channel HS switch (HS=High Side; LS=LowSide). The arrangement according to FIG. 2 comprises a power transistorstructure 102 integrated in a semiconductor body and an evaluating unit103, electrically connected to the former, for overtemperature detectionof the power transistor structure 102. In addition to the powertransistor structure 102, a reverse-biased bipolar diode structure 104is also integrated in the semiconductor body, which is fed from acurrent source 107 located in the separate evaluating unit 103 via anadditional body or bulk terminal 105 on the semiconductor body by areference current 106 in the reverse direction of the diode structure104. The diode structure 104 can be formed, e.g., by the bulk draindiode always present in a MOSFET. The usual short circuit between sourceand bulk does not exist in this and the following embodiments.

The measuring voltage 108 dropped accordingly across the diode structure104 and dependent on the temperature of the diode structure 104 and thuson the temperature of the semiconductor body and thus, in turn, on thetemperature of the power transistor structure 102 is compared with acomparison voltage 109 in the evaluating unit 103 in order to generatefrom this a signal 110 identifying an overtemperature. In thisarrangement, the voltage 109 of a voltage source 112, present at oneinput of a comparator 111, is compared with the voltage 108 at the bodyterminal 105 of the diode structure 104. If the voltage at the bodyterminal 105 of the diode structure 104 exceeds the permanently presetvalue of the reference voltage source 112, the signal state at theoutput of the comparator 111 changes and generates the signal 110identifying an overtemperature of the power transistor. In this way, thediode structure 104 is used as temperature sensor for the temperature ofthe power transistor structure 102, the diode structure 104 beingoperated in the reverse direction with an impressed current.

This makes use of the fact that the reverse current of the diodestructure, detected by an evaluating unit, is exponentially dependent onthe temperature so that the temperature in the semiconductor body can beinferred from the reverse current. If the reverse current of the diodestructure 104 exceeds the current 106 predetermined by the currentsource 107, the voltage at the body terminal 105 changes and the voltagedrop across the diode structure 104 drops. In consequence of thisprocess, the comparator 111 generates the overtemperature signal 110 asdescribed. However, this reverse current exhibits a significant, that isto say analyzable, amount only at high temperatures due to theexponential characteristic, so that the signal deviation of such a diodestructure temperature sensor is small.

Although it is possible to partially compensate for this disadvantage byconstructing the diode structure with the greatest possible area, thisruns counter to the general demand for the highest possible degree ofminiaturization of semiconductor components. In addition, diodestructures always have a barrier layer capacitance in which a charge isstored. This stored charge can cause a current which may be greater thanthe reverse current used for temperature detection which unacceptablyinfluences the measurement result.

Furthermore, the power transistor structure can also be arranged asp-channel LS switch in the arrangement according to FIG. 2. Theaforementioned disadvantages with regard to temperature range, signaldeviation also exist in this case.

For determining the internal temperature of a semiconductor component, adiode structure may be provided in the same semiconductor body in whichthe semiconductor component is integrated, the diode structure beingoperated by an impressed current in its forward direction. The circuitarrangement according to FIG. 3 again comprises a power transistorstructure 102 integrated in a semiconductor body and an evaluating unit103 electrically connected to the former, for detecting overtemperatureof the power transistor structure 102 which is only used forrepresenting the basic principle in this case. In addition to the powertransistor structure 102, a bipolar diode structure 104 is again alsointegrated in the semiconductor body, which diode structure is fed fromthe current source 107 located in the separate evaluating unit 103 viathe additional body terminal 105 at the semiconductor body via thereference current 106 in the forward direction of the diode structure104 compared with FIG. 2.

The voltage 108 correspondingly dropped across the diode structure 104,which is dependent on the temperature of the diode structure 104 andthus on the temperature of the semiconductor body and thus, in turn, onthe temperature of the power transistor structure 102 is again comparedwith a comparison voltage 109 in the evaluating unit 103 in order togenerate from this, analogously to the circuit arrangement in FIG. 2, asignal 110 identifying an overtemperature. Apart from the exemplaryembodiment of the power transistor structure 102 as n-channel HS switch,the power transistor structure 102 in FIG. 3 can also be constructed asp-channel LS switch.

The disadvantageous effect is here that for such an arrangement of thediode structure 104 according to FIG. 3, in the case of an n-channel LSswitch, the corresponding supply voltage is not constantly applied tothe drain terminal of the power transistor structure 102 but that, dueto, e.g., switching processes of the power transistor structure, thevoltage 108 dropped across the diode structure 104 in dependence on thetemperature is subject to large voltage swings. An additionaldisadvantageous factor is that, for the arrangement according to FIG. 3,in the case of a p-channel HS switch, ground potential is not constantlyapplied to the drain terminal of the power transistor structure 102 but,due to, e.g., switching processes of the power transistor structure, thevoltage 108 dropped across the diode structure 104 in dependence ontemperature is also subject to large voltage swings. It is also adisadvantageous factor that the opening of the bulk-source short circuitproduced by the diode structure 104 also being integrated no longerguarantees the dielectric strength of the power transistor. At a highvoltage between drain and source of the power transistor structure 102,this can lead to a voltage breakdown which takes place at a lowervoltage than defined by the voltage class of the power transistorstructure which is specified with the bulk short circuited with thesource. In addition, the high voltage between source and drain producesa high voltage between collector and emitter of an NPN transistor formedfrom two individual diode structures.

The circuit diagram according to FIG. 4 shows a power transistor 1,constructed as n-channel LS switch, including a parasitic diodestructure 8, which is always present when MOS technology is used, whichis located in the reverse direction between bulk terminal 15 and drainterminal 9. The parasitic diode structure 8 can be formed by thebulk-drain diode always present in MOS transistors.

Compared with FIG. 3, the arrangement according to FIG. 4 thusadditionally takes into consideration the parasitic diode structure 8which always exists in MOS transistors but which was neglected in thepreceding figures. In this arrangement, a power transistor structure 7is connected with its drain terminal 9 via an external load resistor 10to a positive supply potential 11 and with its source terminal 12 toground potential, as a result of which a load current 13, flowing intothe drain terminal 9 of the power transistor structure 7, can begenerated in dependence on a voltage, not designated in greater detailhere, on the gate terminal of the power transistor structure 7.Furthermore, the co-integrated diode structure 2 (e.g. the bulk-sourcediode which must not be short circuited in the present case) isconnected in series opposition to the parasitic diode structure 8 (e.g.the bulk-drain diode) and the diode structures 2 and 8 are connected inparallel with the load path of the power transistor structure 7. Abulk-source diode structure 2 is operated in the forward direction withan impressed current 14 as a result of which a voltage 16 dropped acrossthe diode structure 2 is generated.

This voltage 16 is not equal to the load path voltage of the powertransistor structure 7 and is used for overtemperature detection of thepower transistor. Furthermore, the voltage across the load path at drain9 is compared with a preset voltage value 17 of a reference voltagesource 18. In the present case, this comparison takes place via acomparator 19, to the inverting input of which the preset comparisonvoltage 17 is applied and the non-inverting input of which is connectedto the drain terminal 9 of the power transistor structure 7 of thesemiconductor body 1. The comparator 19 can suitably have a switchingcharacteristic with hysteresis.

If the voltage present at the drain terminal 9 of the power transistorstructure 7 exceeds the value of the comparison voltage 17, the state ofthe signal at the output of the comparator 19 changes and short circuitsthe diode structure 2 via a transistor structure 49. A short circuit ofthe diode structure 2 also takes place due to the switching-through ofthe transistor structure 49 if then a control signal “OFF” is activated,this control signal “OFF” and the output of the comparator 19 beinglinked via an OR gate 63 preceding the gate of the transistor structure49.

It has an advantageous effect that the bulk-source diode (co-integrateddiode structure 2) can be used as sensor element for the temperaturemeasurement without reducing the dielectric or break-down strength ofthe power transistor. This is achieved by the fact that the bulk-sourceshort circuit of the power transistor is only temporarily opened for apermissible range of the voltage, predetermined by the reference voltage17, at the drain of the power transistor which is below the hazard limitfor the effects mentioned above. It also has an advantageous effect thatno current flow generated by the impressed current 14 takes place at thesource and the drain output of the power transistor if this is switchedoff (active “OFF” signal). It also has an advantageous effect that atemperature measurement is now possible with the power transistorswitched on and thus a low load path voltage between drain and source ofthe power transistor (voltage at drain 9 lower than reference voltage17). A further possible embodiment is obtained from specifying a maximumpermissible voltage at the load path for the temperature measurement,which can also be monitored by measuring the operating voltage, forexample in bridge circuits.

The circuit diagram of FIG. 5 shows the basic principle of anarrangement with a power transistor constructed as p-channel HS switch,including the parasitic diode structure 8, which is always present whenusing MOS technology, which is located in the reverse direction betweendrain terminal 9 and bulk terminal 15 (parasitic drain-bulk diode), andthe diode structure 2 (source-bulk diode). The evaluating unit alsoshown corresponds to that of FIG. 4 and is only slightly less adapted tothe changed application.

The arrangement according to FIG. 5 again comprises the parasitic diodestructure 8. The power transistor structure 7 is now connected with itsdrain terminal 9 to ground via an external load resistor 10 andconnected to a positive supply potential 11 with its source terminal 12,as a result of which a load current 13 flowing from the drain terminal 9of the power transistor structure 7 is generated in dependence on thevoltage at the gate terminal. Furthermore, the co-integrated diodestructure 2 (source-bulk diode) is connected in series opposition to theparasitic diode structure 8 (drain-bulk diode) and the diode structures2 and 8 are connected in parallel with the load path of the powertransistor structure 7.

In this arrangement, the source-bulk diode structure 2 is operated withthe impressed current 14 in the forward direction, as a result of whichthe voltage 16 dropped across the diode structure 2 is generated. Thisvoltage 16 is used for overtemperature detection of the powertransistor. Furthermore, the voltage at the drain terminal 9 of thepower transistor is compared with the preset voltage value 17 of thereference voltage source 18. In the present case, this comparison ismade via the comparator 19, to the positive input of which the presetcomparison voltage 17 is applied and the negative input of which isconnected to the drain terminal 9 of the power transistor structure 7.The comparator 19 can suitably have a switching characteristic withhysteresis.

If the voltage across the load path exceeds the value of the comparisonvoltage 17, the state of the signal at the output of the comparator 19changes and short circuits the diode structure 2 via the transistorstructure 49. A short circuit of the diode structure 2 due to theswitching-though of the transistor structure 49 also occurs when thecontrol signal “OFF” is activated, this control signal “OFF” and theoutput of the comparator 19 being linked via the NOR gate 68 precedingthe gate terminal of the transistor structure 49. This again results inthe same advantageous effects as in the arrangement from FIG. 4. Theoperating voltage can also be monitored again, e.g. in bridge circuits,in order to prevent the maximum permissible load path voltage possiblybeing exceeded whilst the bulk-source short circuit is opened at thesame time.

The circuit arrangement according to FIG. 6 comprises a power transistorstructure 7 integrated in a semiconductor body 1 and an evaluating unit3, which is electrically connected to the former but is spatiallyseparate and thermally decoupled from it, for overtemperature detectionof the power transistor structure 7. In the power transistor structure7, which, in the present case, is an n-channel MOS field effecttransistor but could equally be a bipolar transistor, IGBT, thyristoretc., a bipolar diode structure 2 is co-integrated in the semiconductorbody 1 in addition to the power transistor structure 7, which diodestructure is fed from a current source 5 located in the separateevaluating unit 3 via an additional body or bulk terminal 15 at thesemiconductor body 1 by a reference current 14 in the forward directionof the diode structure 2. The voltage 16 correspondingly dropped acrossthe diode structure 2, dependent on the temperature of the diodestructure 2 and thus on the temperature of the power transistorstructure 7, is compared with a comparison voltage 22 in the evaluatingunit 3 in order to generate from it a signal 20 identifying anovertemperature. In this way, the diode structure 2 (the bulk-sourcediode in the case shown) is used as temperature sensor for thetemperature of the power transistor structure 7, the diode structure 2being operated in the forward direction with an impressed current.

FIG. 6 also comprises the parasitic bulk-drain diode structure 8 whichis always present when MOS technologies are used, and forms a bipolartransistor together with the diode structure 2. A device of comparator65 and reference voltage source 64 for monitoring the load path voltageat the drain 9 is also contained therein.

The circuit arrangement according to FIG. 6 additionally contains amonitoring circuit with a reference voltage source 64 for generating areference voltage 67, a comparator 65 (possibly with hysteresis) and anMOS field effect transistor 66. In this arrangement, the non-invertinginput of the comparator 65 is connected to the drain terminal 9 of thepower transistor structure 7 and the reference voltage 67 is present atthe inverting input of the comparator 65. The output of the comparator65 is connected to the gate of the transistor 66. The drain terminal ofthe transistor 66 is connected to the body terminal 15 of thesemiconductor body 1 and the current source 5 whilst the source terminalof the transistor 66 is connected to ground.

The monitoring circuit has the purpose of monitoring the amplitude ofthe voltage at the drain terminal 9 of the power transistor structure 7and comparing it with the preset reference voltage 67. In this way, anexcessive voltage at the drain terminal 9 of the power transistorstructure 7 is detected which, with the bulk-source short circuit beingopened at the same time and the dielectric strength of the semiconductorstructure 1 thus being reduced, can lead to its destruction. Thereference voltage 67 can be selected to be very low so that temperaturedetection is only carried out when the load path, represented by theresistor 10, via the power transistor structure 7 is connected. Thereference voltage 67 can also assume higher values as long as its valueis below the critical maximum load path voltage leading to adestruction, which is reduced by the source-bulk short circuit beingopened.

If then the voltage to ground, present at the drain terminal 9, exceedsthe value of the reference voltage 67, for example because the load pathis not connected, the gate of the transistor 66 is driven via the outputof the comparator 65 and the diode structure 2 is short circuited viathe transistor 66 as a result of which the current used forovertemperature detection (largely) does not flow through the diodestructure 2 but (largely) flows through the source-drain path of thetransistor 66. In this case, however, the signal 20 cannot be used as ameasure of an overtemperature detection since the voltage 16 droppedacross the short circuited diode structure 2 is then always very lowindependently of the actual temperature of the power transistorstructure 7 and the voltage 16 is thus always lower than the voltage 22used for the comparison and for detecting an overtemperature.

The effect, which can be reproduced quantitatively, that the voltageoccurring at a diode structure operated in the forward direction withthe impressed current depends on the temperature of this diode structureis utilized in such a manner that due to the conductance of the diodestructure, which rises with temperature, the voltage dropped across thediode structure with a constant impressed current is reduced. Theforward voltage of a diode structure changes linearly with about −2 mVper degree Celsius (.degree. C.).

The diode structure 2 used for temperature measurement is co-integratedinto the semiconductor body 1 in such a manner that, in operation, it isessentially subject to the same heating as the power transistorstructure 7 itself and thus can be used as a measure of the operatingtemperature of the power transistor structure 7 and thus forovertemperature detection of the power transistor structure 7. Theadditional, externally accessible body or bulk terminal 15 is providedat the semiconductor body 1 for the purpose of feeding the current 14into the diode structure 2 and for measuring the voltage 16 droppedacross this diode structure 2 (in the case of an external evaluatingcircuit as in the present case).

In the circuit arrangement according to FIG. 6, the diode structure 2 isconnected in the forward direction between body and ground. A furtherdiode structure 8 is located between body (and thus body terminal 15)and drain terminal 9 of the power transistor structure 7, this being theparasitic bulk-drain diode structure always present. In thisarrangement, the power transistor structure 7 is connected with itsdrain terminal 9 with a positive supply potential 11 via an externalload resistor 10 and with its source terminal 12 to ground potential asa result of which a load current 13 flowing into the drain terminal 9 ofthe power transistor structure 7 can be generated.

As already explained, the circuit arrangement according to FIG. 6comprises a current source 5 for generating the impressed current 14 forthe diode structure 2 and additionally a first embodiment of acomparison circuit 4 for comparing the voltage 16 dropped across thediode structure 2 with a preset comparison voltage 22. In the presentcase, the comparison circuit 4 consists of a comparator 19, to thepositive input of which a preset comparison voltage 22 generated by acircuit 21 is applied and the negative input of which is connected tothe terminal 15 of the semiconductor body 1 and to which voltage 16dropped across the diode structure 2 is thus applied. The comparator 19can suitably have a switching characteristic with hysteresis.

In this arrangement, the circuit 21 is constructed in such a manner thatthe comparison voltage 22 generated by it is temperature-dependent, insuch a manner that an increase in temperature of the evaluating unit 3,and thus an increase in temperature of the circuit 21, leads to anincrease in the comparison voltage 22 generated from it.

An increase in temperature of the evaluating unit 3 occurs, for example,if the ambient temperature increases at which the evaluating unit 3 andcorrespondingly also the semiconductor body 1 are operated. This is thecase, for instance, in applications in a motor vehicle wheresemiconductor bodies and circuits used in the engine compartment areheated to a different degree by radiation of engine heat in dependenceon the operating state and weather-related external temperatures. Inthis manner, the limit value of the overtemperature to be determined canbe automatically adapted to the prevailing ambient temperatures, forexample reduced, in order thus to take into account, for example, thecircumstance that a value of the overtemperature which is critical ordamaging for the operation is lower at high ambient temperatures than atlow ambient temperatures.

The prerequisite for taking the ambient temperature into considerationwith sufficient accuracy is that the semiconductor body 1 and theevaluating unit 3 are thermally decoupled but are placed so close to oneanother spatially that the same ambient temperature is applied to them.However, thermally decoupling also means, in particular, that the twoare not so close that the heat dissipation of the power transistorinfluences the ambient temperature in the area of the evaluatingcircuit. In applications in which this ambient temperature is generated,for example by a heat-radiating source such as a motor vehicle engine,this ambient temperature changes very rapidly with distance from thesource and a spatially more separate arrangement of the semiconductorbody 1 and the evaluating unit 3 would not achieve the desired effect.

According to FIG. 6, the circuit 21 for generating the comparisonvoltage 22 comprises an MOS field effect transistor 39, an MOS fieldeffect transistor 40, a bipolar transistor 41 and a bipolar transistor42 and a resistor 23, a resistor 43 and a resistor 46. The transistor 39is a p-channel MOS field effect transistor and connected with its sourceterminal to a positive supply potential 47 and to the source terminal ofthe transistor 40 which is also of the p-channel type. The drainterminal of the transistor 39 is connected to the gate terminal of thetransistor 39 and to the collector terminal of the transistor 41;similarly, there is a connection between the gate terminal of thetransistor 39 and the gate terminal of the transistor 40. The drainterminal of the transistor 40 is connected to the collector terminal ofthe transistor 42 which, in turn, is connected to the base terminal ofthe transistor 42 and to the base terminal of the transistor 41.Furthermore, the emitter terminal of the transistor 42 is connected tothe resistor 46 and the emitter terminal of the transistor 41 isconnected to the resistor 46 via the resistor 43. The two resistors 46and 23 represent a voltage divider, the comparison voltage 22 droppedacross the resistor 23 being applied to the positive input of thecomparator 19.

With a rising ambient temperature acting on the evaluating unit 3 andthus on the components contained in this evaluating unit 3, linearlyincreasing currents through a first resistor 23, a second resistor 43and a third resistor 46 are generated in the circuit 21. As a result, avoltage drop 22 rising linearly with the temperature is generated at thefirst resistor 23, which, in the present embodiment, is used ascomparison voltage 22 for later comparison by the comparator 19 with thevoltage 16 dropped across the diode structure 2, applied to the negativeinput of the comparator 19.

In this way, an increase of the ambient temperature acting on theevaluating unit 3, by increasing the comparison voltage 22, leads to areduction in the difference between the voltage 16 at the diodestructure 2 and the comparison voltage 22 as a result of which the limitvalue for detection of an overtemperature of a power transistorstructure 7 is reached earlier. The heating of the semiconductor body 1,and thus of the power transistor structure 7, necessary for reaching theovertemperature is less for high ambient temperatures. At low ambienttemperatures, a greater range of heating of the power transistorstructure 7 is thus permitted (temperature swing) than is the case athigh ambient temperatures.

Corresponding to the circuit arrangements according to FIG. 4 and FIG.5, the voltage 16 at the diode structure 2 and a comparison voltage 22are again compared by the comparator 19. The comparison voltage 22 andthe impressed current 14 are selected in such a manner that the voltage16 dropped across the diode structure 2 at permissible operatingtemperatures of the semiconductor body 1 is greater than the comparisonvoltage 22 preset in the evaluating unit 3. If the voltage 16 droppedacross the diode structure 2 exceeds the value of the comparison voltage22 with increasing temperature of the semiconductor body 1, and if thevoltage 16 is thus lower than the comparison voltage 22, the state ofthe signal 22 at the output of the comparator 19 changes and thusindicates that an overtemperature of the power transistor structure 7has been reached. In this case, as stated above, the limit value of theovertemperature to be determined is not preset but is dependent on theambient temperature acting on the circuit arrangement 21.

The circuit arrangement according to FIG. 7 again contains asemiconductor body 1 and an external, thermally decoupled evaluatingunit 3. The structure of the power transistor structure 7 and of thediode structures 2 and 8 is identical with that shown in FIG. 6. Incontrast to the embodiments described above, the voltages used fordetecting an overtemperature are first converted into correspondingcurrents, namely voltage 16 into current 25 and comparison voltage 28into current 26, for the purpose of the evaluation.

This is achieved by a voltage/current converter 24 for converting avoltage 16 dropped across the diode structure 2 into a current 25 and bya voltage/current converter 27 for converting a comparison voltage 28into a current 26. In this arrangement, the voltage/current converters24 and 27 are initially reproduced as abstract circuit blocks in FIG. 7.The current 25 generated by the voltage/current converter 24 and thecurrent 26 generated by the voltage/current converter 27 are subtractedat a node 29 and, if necessary, converted into a voltage. The resultantcurrent or the resultant voltage, respectively, are again evaluated by ausing a comparator 19 (for example by a comparison with zero).

If the first current 25 generated by converting the voltage 16 measuredat the diode structure 2 falls below the value of the second current 26generated by converting the comparison voltage 28 due to a temperatureincrease, the state of the signal at the output 20 of the comparator 19changes and thus indicates that an overtemperature of the powertransistor structure 7 has been reached. The limit value of theovertemperature to be determined can be selected freely by suitablychoosing the preset comparison voltage 28.

FIG. 8 shows a development of the circuit arrangement shown in FIG. 7,with voltage/current converter 24 and voltage/current converter 27. Inthis arrangement, the voltage/current converter 24 contains anoperational amplifier 30, an MOS field effect transistor 31, an MOSfield effect transistor 35 and a resistor 32 across which a voltage 33proportional to the voltage 16 dropped across a diode structure 2 isdropped. In the voltage/current converter 24, the gate terminals of thetwo transistors 31 and 35 are connected to the output of the operationalamplifier 30, the source terminals of the transistors 31 and 35 alsobeing connected to one another and being connected to the positivesupply potential 34. The drain terminal of the transistor 31 isconnected to ground via the resistor 32. The voltage 33 dropped acrossthe resistor 32 is fed back to the non-inverting input of theoperational amplifier 30, at the inverting input of which the voltageacross the diode structure 2 is present. The operational amplifier 30corrects the voltage 33 across the resistor 32 in such a manner that itis equal to the voltage across the diode structure 2. The currentthrough the source/drain path of the transistor 31 is thus equal to theratio of voltage 33 to the value of the resistor 32. Accordingly, thecurrent through the source-drain path of the transistor 35, forming theoutput current, is then proportional to the current through thesource/drain path of the transistor 31 and proportional to the voltageacross the diode structure 2, the output current thus becoming lowerwith increasing temperature of the semiconductor body 1.

The drain terminal of the second transistor 35 is connected to a node 29so that the current 25 from the voltage/current converter 24 acting ascurrent source flows into the node 29, a current 26 flowing off againvia the voltage/current converter 27 acting as current sink so that thedifference between the two currents can be evaluated by the comparator19 (for example by comparison with a fixed threshold or zero). Thevoltage/current converter 27 is that from the circuit 21, explained inFIG. 6, for generating an ambient-temperature-dependent referencevoltage. Accordingly, the circuit 21 again contains the transistor 39,transistor 40, transistor 41 and transistor 42, resistor 43 and resistor45. In addition, an MOS field effect transistor 36, an MOS field effecttransistor 37 and an MOS field effect transistor 38 are provided in theexemplary embodiment according to FIG. 9.

A current, which is proportional to the current 48 through thesource-drain path of the transistor 39 flows through the source-drainpath of the transistor 38, the source and gate terminals of which are ineach case connected to the source and gate terminals of transistor 40,in the manner of a current mirror, just like it does through thesource-drain path of transistor 40, so that a current rising linearlywith the ambient temperature of the evaluating unit 3, which is definedby the ratio of the voltage 44 dropped across the resistor 43 and theresistance value of the resistor 43, is provided.

The current provided by the transistor 38 is then mirrored by means of a(further) current mirror consisting of transistors 36 and 37, in such amanner that the current 26 flowing off from the node 29 is generated.Due to the current 48 being mirrored twice in the voltage/currentconverter 27, the current 26 is thus produced which also rises linearlywith the ambient temperature of the evaluating unit 3.

From the current 25, depending linearly on the voltage 16 at the diodestructure 2 and becoming lower with rising temperature of thesemiconductor body 1, the current 26 becoming greater with ambienttemperature is subtracted at the node 29. The node 29 is connected tothe comparator 19 so that the difference produced by subtracting thecurrents 25 and 26 at the comparator 19 is a measure of whether theoperating temperature of the power transistor structure 7 integrated inthe semiconductor body 1 is permissible or not, the relevant limit valuebeing dependent on the ambient temperature represented by the current26.

If the current 25 drops below the current 26 (for example in the case ofthe zero-point comparison: current 25−current 26<0), the state of thesignal 20 at the output of the comparator 19 changes and thus indicatesthat an overtemperature of the power transistor 7 has been reached. Theheating of the power transistor structure 7 necessary for reaching theovertemperature is thus less at higher ambient temperatures ofsemiconductor body 1 and evaluating unit 3.

According to the embodiment, a greater heat range of the powertransistor structure 7 (temperature swing) is permitted at the same timeat low ambient temperatures of the semiconductor body 1 and theevaluating unit 3 than is the case at higher ambient temperatures. Asignificant advantage consists in that, due to the use of identicalmaterials and possibly identical dimensions in the resistors 32 and 43,the absolute accuracy tolerances of these resistors compensate for thetemperature dependences reducing the measuring accuracy and thus allowthe absolute accuracies to be distinctly increased.

The circuit arrangement according to FIG. 8 also contains a monitoringcircuit 52 with a reference voltage source for generating a referencevoltage 50, a comparator 51 (possibly with hysteresis) and an MOS fieldeffect transistor 49. In this arrangement, the non-inverting input ofthe comparator 51 is connected to the drain terminal 9 of the powertransistor structure 7 and a reference voltage 50 is present at theinverting input of the comparator 51. The output of the comparator 51 isconnected to the gate of the transistor 49. The drain terminal of thetransistor 49 is connected to the body terminal 15 of the semiconductorbody 1 and the current source 5 while the source terminal of thetransistor 49 is connected to ground.

It is the purpose of the monitoring circuit 52 to monitor the magnitudeof the voltage at the drain terminal 9 of the power transistor structure7 and to compare it with a preset reference voltage 50. In this way, anexcessive voltage at the drain terminal 9 of the power transistorstructure 7 is detected which, with the bulk-source short circuit beingopened at the same time and the dielectric strength of the semiconductorstructure 1 thus being reduced, can lead to its destruction. Thereference voltage 50 can be selected to be very low in order to carryout temperature detection only when the load path, represented by theresistor 10, is connected via the power transistor structure 7. Thereference voltage 50 can also assume higher values as long as its valueis below the critical maximum load path voltage leading to adestruction, which is reduced by opening the source-bulk short circuit.

If then the voltage to ground, present at the drain terminal 9, exceedsthe value of the reference voltage 50, for example because the load pathis not connected, the gate of the transistor 49 is driven via the outputof the comparator 51 and the diode structure 2 is short circuited viathe transistor 49 as a result of which the current used forovertemperature detection (largely) does not flow through the diodestructure 2 but (largely) flows through the source-drain path of thetransistor 49. With the load path switched off, the current at the drainterminal 9 is very low in any case. In this case, however, the signal 20cannot be used as a measure of overtemperature detection since then thevoltage 16 dropped across the short circuited diode structure 2 isalways very low independently of the actual temperature of the powertransistor structure 7 and the current 25 is thus always lower than thecurrent 26 used for the comparison and for detecting an overtemperature.For the case of restoring the source-bulk short circuit with anexcessive voltage at the drain 9, it is then no longer possible tomonitor the temperature. This state is obtained, for example, with avery high load (short circuit) or a normal switching-off process. Sincethe temperature monitoring is used in any case for switching off theswitch with an excessive temperature and to prevent further power input,this behavior does not have a disadvantageous effect. The dielectricstrength of the power transistor, which, in the normal case, is presentdue to the bulk-source short circuit with the technology used, which isno longer given by using the co-integrated diode structure 2 in thepresent case, is restored by short circuiting the diode structure 2 viathe transistor 49 with excessive voltage values at the drain.

In the circuit arrangement according to FIG. 9, a further embodiment ofa circuit for overtemperature detection of a power transistor structure7 with a monitoring circuit 52, extended with respect to FIG. 8, and afurther embodiment of the voltage/current converter 27 is provided.Semiconductor body 1 and voltage/current converter 24 correspond tothose shown in FIG. 8.

The monitoring circuit 52 contains an inverter 53, an OR gate 54 and anMOS field effect transistor 49. A logical input signal is fed in at aterminal 55 of the evaluating unit 3 in order to be able to activate anddeactivate the evaluating circuit 3 from the outside. Compared with theembodiment according to FIG. 8, the output of the comparator 51 is notconnected directly to the gate terminal of the transistor 49 butinitially to a first input of the OR gate 54. The terminal 55 isconnected to the input of the inverter 53, the output of which isconnected, in turn, to a second input of the OR gate 54, the output ofthe OR gate 54 being coupled to the gate terminal of the transistor 49.

The logic level H (power transistor structure 7: “ON”) at terminal 55 ofthe evaluating unit 3 stands for the case in which the temperaturedetection and the monitoring of the voltage at the drain terminal 9 isto be activated, wherein this level can be generated, for example, by aload connected via the power transistor structure 7. The logic level Hat the terminal 55 is converted into the logic level L by the inverter53 and applied to the second input of the OR gate 54. If the outputsignal of the comparator 51 has the logic level L, that is to say thevoltage at the drain terminal 9 of the power transistor structure 7 isbelow the preset reference voltage 50, the temperature detection iscarried out as described above.

If the output signal of the comparator 51 has the logic level H, that isto say the voltage at the drain terminal 9 of the power transistorstructure 7 is above the preset reference voltage 50 and thus in a rangewhich could result in the destruction of the semiconductor body 1, thediode structure 2 is again short circuited via the transistor 49, drivenby the output signal from the OR gate 54. Such a case is, for example,that of an avalanche in which a bipolar transistor formed from the twodiode structures 2 and 8, which is already active, forms the weak point.The temperature is therefore monitored only in the switched-throughstate of the power transistor structure 7 and/or when the voltage dropsbelow the maximum permissible load path voltage predetermined by thevoltage 50.

If the logic level L (power transistor structure 7: “OFF”) is present atterminal 55 of the evaluating unit 3, temperature detection isdeactivated. In this event, the logic level L at terminal 55 is firstconverted into the logic level H via the inverter 53 and applied to thesecond input of the OR gate 54. Independently of the value of the levelpresent at the first input of the OR gate 54 (from output of thecomparator 51), a signal with the logic level H is thus generated inevery case at the output of the OR gate 54 and the diode structure 2 isagain short circuited via the transistor 49. As stated above, the signal20 cannot be used for overtemperature detection in all cases in whichthe diode structure 2 is short circuited via the transistor 49.

FIG. 9 also shows a further embodiment of the voltage/current converter27 from FIG. 7 which has a supply potential 47, a resistor 56, aresistor 61, a bipolar transistor 57, a bipolar transistor 58, a bipolartransistor 59 and a bipolar transistor 60. In this arrangement, thetransistor 57 is connected with its collector terminal to the supplypotential 47 via the resistor 56. The base terminal of the transistor 57is connected to the base terminal of the transistor 58 and to thecollector terminal of the transistor 57. The collector terminal of thetransistor 58 is connected to the node 29 at which the current 25 fromthe voltage/current converter 24 and the current 26 into thevoltage/current converter 27 are subtracted from one another for thepurpose of evaluation by the comparator 19 and thus for generating thesignal 20. Furthermore, the emitter terminal of the transistor 57 isconnected to the collector terminal of the transistor 59, the emitterterminal of the transistor 58 is connected to the collector terminal ofthe transistor 60, the emitter terminal of the transistor 57 isconnected to the base terminal of the transistor 60 and the emitterterminal of the transistor 58 is connected to the base terminal of thetransistor 59. The emitter terminal of the transistor 59 is connecteddirectly to ground; the emitter terminal of the transistor 60 isconnected to ground via the resistor 61. The limit value of theovertemperature is again dependent on the ambient temperature at theevaluating unit 3. Similarly, by suitably using resistor components ofthe same material for the resistors 32 and 61 in the voltage/currentconverters 24 and 27, the absolute accuracy tolerances of theseresistors and thus different temperature dependences reducing themeasuring accuracy are again compensated for and the absolute accuracyof the overtemperature detection is thus distinctly increased.

The exemplary embodiments do not show start-up circuits which could benecessary under some circumstances when switching on the circuitarrangement but which do not have any significance for the basicfunction of the circuit arrangement and have therefore been omitted forthe sake of clarity. The expert can however easily use known start-upcircuits for the respective purpose.

While the invention disclosed herein has been described in terms ofseveral different embodiments, there are numerous alterations,permutations, and equivalents which fall within the scope of thisinvention. It should also be noted that there are many alternative waysof implementing the methods and compositions of the present invention.It is therefore intended that the following appended claims beinterpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

1. A circuit arrangement for detecting the overtemperature of asemiconductor body, the circuit arrangement comprising: at least onefield effect transistor including a load terminal; a parasitic diodeintegrated in the semiconductor body, the parasitic diode connecting theload terminal of the field effect transistor to a bulk terminal of thesemiconductor body; an evaluating unit electrically connected to theparasitic diode via the bulk terminal at the semiconductor body, theevaluating unit configured to feed a current into the parasitic diodeand evaluate a temperature-dependent voltage drop across the parasiticdiode, the direction of the current fed into the diode being such thatit is operated in the forward direction; wherein the evaluating unitcomprises a short circuit device operable to temporarily short circuitthe parasitic diode.
 2. The circuit arrangement as claimed in claim 1wherein the field effect transistor is provided as a power transistorstructure.
 3. The circuit arrangement as claimed in claim 1, wherein thefield effect transistor provides a power transistor structure, whereinthe short circuit device is configured to short circuit the parasiticdiode when the field effect transistor is switched on and a voltageoccurs along a drain-source path of the power transistor structure whichis above a preset comparison voltage.
 4. The circuit arrangement asclaimed in claim 1, wherein the short circuit device is configured toshort circuit the parasitic diode when the field effect transistor isswitched off and a voltage occurs at a drain terminal of the powertransistor structure which is above a preset comparison voltage.
 5. Thecircuit arrangement as claimed in claim 1, wherein the short circuitdevice is configured to short circuit the parasitic diode if anoperating voltage, which is above a preset comparison voltage, providesfor an excessive voltage at a drain terminal of the power transistorstructure.
 6. The circuit arrangement as claimed in claim 1, wherein theshort circuit device includes a switching element, and wherein theevaluating unit is an external evaluating unit, the short circuit devicebeing arranged in the external evaluating unit.
 7. The circuitarrangement as claimed in claim 1, wherein the field effect transistorincludes a load path, wherein the parasitic diode is connected to afurther parasitic diode as diodes in series opposition, and wherein thediodes in series opposition are connected in parallel with the load pathof the field effect transistor.
 8. The circuit arrangement as claimed inclaim 1, wherein the evaluating unit is thermally decoupled and arrangedseparately from the semiconductor body.
 9. The circuit arrangement asclaimed in claim 1, wherein the evaluating unit is configured to comparethe voltage drop across the parasitic diode with a preset comparisonvoltage.
 10. The circuit arrangement as claimed in claim 1, wherein theevaluating unit is configured to compare the voltage drop across a diodestructure in the evaluating unit with a comparison voltage dependent onthe temperature of the evaluating unit.
 11. The circuit arrangement asclaimed in claim 9, wherein the evaluating unit is configured togenerate an overtemperature detection signal when a predeterminabledifference of the voltage drop across the parasitic diode and the presetcomparison voltage is reached.
 12. The circuit arrangement of claim 10,wherein the evaluating unit comprises current/voltage convertersconfigured to convert the voltage drop across the diode structure and/orthe comparison voltage into currents.
 13. The circuit arrangement asclaimed in claim 12, wherein the evaluating unit is configured togenerate an overtemperature detection signal when a predetermineddifference of the currents is reached.
 14. The circuit arrangement asclaimed in claim 10, wherein the current/voltage converters compriseresistor components of the same material.
 15. The circuit arrangement asclaimed in claim 1, wherein the voltage across a load path of the fieldeffect transistor is monitored.
 16. The circuit arrangement as claimedin claim 1, wherein the evaluating unit is configured to be activated ordeactivated by an external signal.
 17. The circuit arrangement asclaimed in claim 1, wherein the parasitic diode is a source-bulk diodeinherent in the field effect transistor.
 18. The circuit arrangement asclaimed in claim 7, wherein the further parasitic diode is a drain-bulkdiode inherent in the field effect transistor.